Conventionally, when an electronic circuit board or the like is produced, a nickel film is formed on the surface of a substrate to form a nickel circuit pattern thereon. For example, as a film-forming technology for forming such a metal film, there has been proposed a film-forming technology that includes forming a metal film on the surface of a Si semiconductor substrate or the like through a plating process such as an electroless plating process (for example, see Patent Literature 1), or forming a metal film using PVD such as sputtering.
However, when a plating process such as an electroless plating process is performed, it has been necessary to perform water washing after the plating process, as well as processing of a waste liquid that has been produced during the water washing. Meanwhile, when a film is formed on the surface of a substrate using PVD such as sputtering, internal stress is generated in the metal film formed. Thus, there is a limitation in increasing the thickness of the film. In particular, when sputtering is performed, a film may be formed only in a high vacuum in some cases.
In view of the foregoing, there has been proposed a film-forming method for forming a metal film that uses an anode, a cathode, a solid electrolyte membrane disposed between the anode and the cathode, and a power supply unit that applies a voltage across the anode and the cathode (for example, see Patent Literature 2).
The solid electrolyte membrane herein is formed by spin-coating the surface of a substrate with a solution containing a precursor of the solid electrolyte membrane in advance and curing it. The solid electrolyte membrane is impregnated with metal ions for forming a film. Then, a substrate is disposed such that it is opposite the anode and is electrically connected to the cathode, and a voltage is applied across the anode and the cathode so that the metal ions that have impregnated the solid electrolyte membrane are deposited on the cathode side. Accordingly, a metal film made of metal of the metal ions can be formed.